Two-layer adhesion of electronics to a surface

ABSTRACT

Embodiments of the present invention are directed to a two-layer adhesive and methods of using the same to secure an electronic device to an organism. In a non-limiting embodiment of the invention, a surface of the organism is coated with a first adhesive layer (bottom layer). The first adhesive layer is cured and a surface of the cured first adhesive layer is coated with a second adhesive layer (top layer). An electronic device is positioned on the second adhesive layer prior to curing the second adhesive layer. The second adhesive layer is then cured, thereby embedding the electronic device within the second adhesive layer. The bottom layer and the top layer are selected such that the bottom layer releases upon exposure to a first solvent after a first duration and the top layer releases upon exposure to a second solvent after a second duration more than the first duration.

BACKGROUND

The present invention relates generally to wearable, flexible,healthcare and medical related electronics. More specifically, thepresent invention relates to a two-layer adhesive for securing flexiblewearable sensor electronics to a surface of a live organism, including,but not limited to, the organism's fingernails, toenails, teeth, claw,hoof, and skin.

The development of technologies that enable the wireless collection andanalysis of quantitative, clinically relevant information on a patient'sphysiological status is of growing interest. In particular, soft,biocompatible systems are widely regarded as important because theyfacilitate the mounting of wearable sensors on external (e.g., skin ornail) and internal (e.g., heart and brain) surfaces of the body.Wearable sensors allow for the collection and analysis of clinicallyrelevant information directly on the patient, and ultraminiaturized,lightweight, and battery-free wearable devices have the potential toestablish complementary options in biointegration, where longer duration(e.g., months) interfaces are possible on hard surfaces such as thefingernails and the teeth, with negligible risk for irritation ordiscomfort. Some example wearable sensors include strain gauges,temperature sensors, accelerometers, photoplethysmograms (PPGs),electrocardiograms (ECGs), electroencephalography (EEG) devices,respiration sensors, gyroscopes, and piezoelectric sensors.

Strain gauges, for example, are useful for measuring or monitoringstresses, forces, torques and a host of other stimuli includingdisplacement, acceleration and position of the patient's body. Theelectrical conductance of a strain gauge (typically formed of a dopedsilicon or metal) varies with its geometry, such that a deformation ofthe strain gauge results in a change in its electrical resistance. Thestress on a strain gauge can therefore be inferred from a measuredresistance of the strain gauge using a known gauge factor, which is aratio of relative change is resistance to the strain on the test piece.The resistance of the strain gauge can be measured using a Wheatstonebridge.

Regardless of the specific type of wearable sensor used in a givenapplication, an adhesive is typically applied at the interface betweenthe patient and the sensor to bond these wearable sensors to thepatient's body. For example, cyanoacrylate-based adhesives can ensurethe strong adhesion of a strain gauge to a fingernail or toenail.Cyanoacrylates are popular adhesives for wearable sensors because theyoffer a fast drying, semi-permanent bond that can be easily andconformally coated over a portion of the patient's body, such as afingernail.

SUMMARY

Embodiments of the invention are directed to a method for using atwo-layer adhesive to secure an electronic device to a patient (e.g., toa live nail) or an animal (e.g., claw, hoof). A non-limiting example ofthe method includes coating a surface of the nail with a first adhesivelayer (bottom layer). The first adhesive layer is cured and a surface ofthe cured first adhesive layer is coated with a second adhesive layer(top layer). An electronic device is positioned on the second adhesivelayer prior to curing the second adhesive layer. The second adhesivelayer is then cured, thereby embedding the electronic device within thesecond adhesive layer. The bottom layer and the top layer are selectedsuch that the bottom layer releases upon exposure to a first solventafter a first duration and the top layer releases upon exposure to asecond solvent after a second duration more than the first duration.

Embodiments of the invention are directed to a method for removing anelectronic device from a patient (e.g., from a live nail). Anon-limiting example of the method includes forming an adhesive stack ona surface of the patient. The adhesive stack can include a bottom layerpositioned between a top layer and the surface of the patient. Theelectronic device can be embedded in the top layer. The bottom layer andthe top layer are selected such that the bottom layer releases uponexposure to a first solvent after a first duration and the top layerreleases upon exposure to a second solvent after a second duration morethan the first duration. The method can include exposing the adhesivestack to the first solvent for the first duration to release theadhesive stack from the surface of the patient. The method can includeremoving the adhesive stack from the patient.

Embodiments of the invention are directed to an adhesive stack forsecuring an electronic device to a live nail. A non-limiting example ofthe adhesive stack includes a top layer and a bottom layer positionedbetween the top layer and a surface of the live nail. The adhesive stackcan further include an electronic device embedded in the top layer. Thebottom layer and the top layer are selected such that the bottom layerreleases upon exposure to a first solvent after a first duration and thetop layer releases upon exposure to a second solvent after a secondduration more than the first duration.

Additional technical features and benefits are realized through thetechniques of the present invention. Embodiments and aspects of theinvention are described in detail herein and are considered a part ofthe claimed subject matter. For a better understanding, refer to thedetailed description and to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The specifics of the exclusive rights described herein are particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe embodiments of the invention are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 depicts an electronic device attached to a body surface accordingto one or more embodiments of the invention;

FIG. 2 depicts a cross-sectional view of the electronic device and thetwo-layer adhesive shown in FIG. 1 according to one or more embodimentsof the invention;

FIG. 3 depicts a system employing the electronic device shown in FIG. 1according to one or more embodiments of the invention;

FIG. 4 depicts a block diagram for implementing the electronic deviceshown in FIG. 1 according to one or more embodiments of the invention;

FIG. 5 depicts a flow diagram illustrating a method according to one ormore embodiments of the invention; and

FIG. 6 depicts a flow diagram illustrating a method according to one ormore embodiments of the invention.

The diagrams depicted herein are illustrative. There can be manyvariations to the diagram or the operations described therein withoutdeparting from the spirit of the invention. For instance, the actionscan be performed in a differing order or actions can be added, deletedor modified.

In the accompanying figures and following detailed description of thedescribed embodiments of the invention, the various elements illustratedin the figures are provided with two or three-digit reference numbers.With minor exceptions, the leftmost digit(s) of each reference numbercorrespond to the figure in which its element is first illustrated.

DETAILED DESCRIPTION

It is understood in advance that although example embodiments of theinvention are described in connection with a particular wearable sensor(e.g., a strain gauge), embodiments of the invention are not limited tothe particular sensor architectures described in this specification.Rather, embodiments of the present invention are easily capable of beingimplemented to bond a wide range of wearable sensors, such as anaccelerometers, photoplethysmograms (PPGs), electrocardiograms (ECGs),electroencephalography (EEG) devices, gyroscopes, temperature sensors,respiration sensors, piezoelectric sensors, heart-monitoring devices,glucose-monitoring devices, and TENS (transcutaneous electrical nervestimulation) electrode therapy devices, among others, to a body surfaceof an organism, including, for example, the organism's fingernails,toenails, teeth, claw, hoof, and skin.

Turning now to an overview of technologies that are more specificallyrelevant to aspects of the present invention, an adhesive such as acyanoacrylate is commonly used to bond wearable sensors (electronicdevices such as strain gauges) to a patient's body (often a fingernail).An ideal adhesive needs to satisfy several criteria. First, an adhesiveshould be stiff enough to allow viable signals to be read by asensor/monitor. In other words, the young's modulus of the adhesivematerial needs to be large enough to allow deformations to not bedampened. An adhesive should be strong, allowing for the wearable sensorto remain on the patient for as long as needed. To ease application andpatient distress, the adhesive should cure or dry in as short a time aspossible. Similarly, the patient's body should not need to be put intoan awkward position during application, due to patient's comfort as wellas an inability to stay still long enough to allow the application ofthe sensor. Finally, once the wearable sensor is no longer needed, theadhesive should be easily removable, without causing harm to thepatient's body or to the sensor itself (for reusability or furtherstudy).

Cyanoacrylates are ubiquitous as medical device adhesives, particularlywith respect to wearable sensors placed on a patient's fingernail, inpart because the cyanoacrylate family satisfies so many characteristicsof an ideal adhesive. Cyanoacrylates are fast drying (typically around30 seconds) adhesives that can be conformally coated onto a patient'sbody to provide a strong, semi-permanent bond. As a result, many methodsused to attach a sensor to a fingernail rely upon products whose mainingredient is cyanoacrylate.

Cyanoacrylates make excellent adhesives, but they are very difficult toremove. Cyanoacrylates are typically removed using mechanicalforce—scratching off, scoring, scraping, etc. While effective atremoving a cyanoacrylate-based adhesive, these methods are slow, willdamage a patient's nail or skin, and can destroy the wearable sensor.This results in harm to the patient and prevents reuse of the sensor. Tomitigate the damage to the patient and to the electronics and to speedup the removal process, the interface between the patient and thewearable sensor can be soaked in a solvent to release the adhesive.Acetone is typically used as exposure to acetone will soften a driedcyanoacrylate.

Adhesive removal even with a solvent soak, however, can take up to 30minutes or even longer (depending on thickness of application) beforethe adhesive fully releases from the nail. Oftentimes, repeat soakingsin the solvent are needed. This removal process is impractically longand burdensome. In addition, a surface such as a fingernail provides avery limited contact area between the solvent with the adhesive, furtherincreasing removal time and inconvenience. Even worse, prolonged soaksin solvents such as acetone can weaken a nail—resulting in the same typeof damage to the nail that a solvent soak is trying to prevent.

Turning now to an overview of aspects of the present invention, one ormore embodiments of the invention address the above-describedshortcomings of the prior art by providing a new two-layer adhesive forsecuring electronics to a patient's body (nails, skin, teeth, etc.).This two-layer adhesive includes a top adhesive layer and a bottomadhesive layer. The top adhesive layer is a fast drying, permanentbonding material that secures the sensor. As used herein, a “permanent”bonding material includes adhesive materials that require mechanicalforce (scratching off, scoring, scraping, etc.) or long solvent soaks(greater than about 5 minutes) to remove. This top layer can includestrong adhesives such as cyanoacrylates. The bottom adhesive layer is afast drying, temporary bonding material that is applied directly to thepatient's body (e.g., nail) and binds the top adhesive layer to thepatient. As used herein, a “temporary” bonding material includesadhesive materials that can be peeled or wiped off without requiring along solvent soak time (e.g., materials that can be removed after asolvent soak of less than about 5 minutes, or materials that do notrequired any solvent soak). In other words, the material for the bottomadhesive layer is selected to be easily removable, ensuring that thetwo-layer adhesive can be removed from the patient without resorting todamaging mechanical processes or prolonged soak periods (e.g., soaksgreater than 5 minutes).

Advantageously, the bottom adhesive layer prevents the top adhesivelayer from making direct contact with the patient's body. This allowsfor the use of conventionally strong adhesives (e.g., cyanoacrylates)without needing to worry about the difficult removal requirements ofthose adhesives. In other words, this two-layer adhesive inserts aneasily removable temporary adhesion material between a strong, permanentbonding material and the patient's body. Once removed from the patient'sbody, the top adhesive layer and the sensor layer can be soaked in asolvent for separation and eventual reuse of the sensor layer (withoutpatient aggravation).

Turning now to a more detailed description of aspects of the presentinvention, FIG. 1 depicts an electronic device 102 attached to a bodysurface (as shown, a fingernail 104) in accordance with one or moreembodiments of the present invention. In some embodiments of theinvention, multiple instances of the electronic device 102 are attachedto the same or various body surfaces (e.g., to the same fingernail or toa combination of fingernails, toenails, teeth, skin, etc.), optionallyat different orientations/locations. However, embodiments arecontemplated herein where a single electronic device 102 is employed ata single location of a person's body.

In some embodiments of the invention, the electronic device 102 is awearable sensor. For example, the electronic device 102 can be a straingauge. In some embodiments of the invention, the electronic device 102is an accelerometer, photoplethysmogram (PPG), electrocardiogram (ECG),electroencephalography (EEG), temperature sensor, respiration sensor,gyroscope, piezoelectric sensor, heart-monitoring device,glucose-monitoring device, TENS (transcutaneous electrical nervestimulation) electrode therapy device, or any other type of wearabledevice. In some embodiments of the invention, the body surface is thefingernail 104. In some embodiments of the invention, the body surfaceis one or more of a patient's fingernails, toenails, teeth, or skin.Although the body surface depicted in FIG. 1 is a fingernail 104, thetwo-layer adhesion processes and resulting structures described inconnection with the fingernail 104 apply equally to various bodysurfaces, including, for example, toenails, teeth, and skin.

As further shown in FIG. 1 , the footprint of the electronic device 102can be configured to fit on the respective body surface (e.g., 15 mm×15mm or less for a human fingernail 104). For instance, in the presentexample, each sensor (electronic device 102) is smaller than therespective fingernail 104 to which it is attached, thereby enablingmultiple sensors to be attached to the same fingernail 104. In someembodiments of the invention, the footprint (a×b) of the electronicdevice 102 is less than or equal to 15 mm×15 mm, although other sizesare within the contemplated scope of the invention. In other words, theconfiguration shown in FIG. 1 is merely an example, and the number,orientation, and size of the sensors can be adjusted (e.g., thefootprints can be scaled up or down, etc.) depending on the particularapplication.

A magnified view 106 of the electronic device 102 is provided. In someembodiments of the invention, the electronic device 102 is a straingauge sensor having multiple stacked layers. In some embodiments of theinvention, the strain gauge sensor version of the electronic device 102can include a metal sensor wire 108 placed over a flexible substrate110. As will be described in detail below, embodiments of the inventionare contemplated herein where the flexible substrate 110 includes atwo-layer adhesive 112.

As further shown in FIG. 1 , the metal sensor wire 108 can be configuredto have a serpentine layout to increase the available length of themetal sensor wire 108, and hence the resistance. While a serpentinelayout of the metal sensor wire 108 is shown, other configurations arepossible. With the constraints on the overall footprint of theelectronic device 102 (see above), the length of the sensor wire 108 canonly be made so long. In some embodiments of the invention, to furtherincrease the overall resistance, and thereby decrease the total currentand power consumption of the sensor, multiple sensor layers are stacked(not shown). Interconnects can be used to electrically couple thestacked layers.

FIG. 2 depicts a cross-sectional view of the electronic device 102 andthe two-layer adhesive 112 shown in FIG. 1 . As discussed previouslyherein, the electronic device 102 is built on a flexible substrate 110.The flexible substrate 110 can include the two-layer adhesive 112.

In some embodiments of the invention, the two-layer adhesive 112 caninclude a top adhesive layer 114 and a bottom adhesive layer 116. Thetop adhesive layer 114 can include a fast drying, permanent bondingmaterial that secures the metal sensor wire 108. For example, the topadhesive layer 114 can include strong adhesives such as cyanoacrylates.

The bottom adhesive layer 116 can include a fast drying, temporarybonding material that is applied directly to the patient's body (e.g.,fingernail 104). The bottom adhesive layer 116 binds the top adhesivelayer 114 to the fingernail 104. As discussed previously herein, thematerial for the bottom adhesive layer 116 is selected to be easilyremovable, ensuring that the two-layer adhesive 112 can be removed fromthe patient without resorting to damaging mechanical processes orprolonged soak periods (e.g., soaks greater than 5 minutes). In someembodiments of the invention, the bottom adhesive layer 116 is selectedfrom one of three classes of composite materials, described sequentiallybelow.

In some embodiments of the invention, the bottom adhesive layer 116includes a film former, plasticizer, and solubilizing agent (alsoreferred to as a stabilizer). The film former, plasticizer, andsolubilizing agent collectively define a first class of adhesivematerials. In some embodiments of the invention, the film former caninclude polyurethane-35 or acrylic or vinyl pyrrolidone (VP)crosspolymer resins. In some embodiments of the invention, theplasticizer can include glycerine. In some embodiments of the invention,the solubilizing agent can include laureth-21. Forming the bottomadhesive layer 116 from a film former, plasticizer, and solubilizingagent in this manner results in the bottom adhesive layer 116 having anair dry time of about 30 to 300 seconds. Advantageously, a removal timeof only about 3 to 120 seconds can be achieved using only a water soak.The bottom adhesive layer 116 can be removed after the water soak bypeeling or rubbing.

In some embodiments of the invention, the bottom adhesive layer 116includes a film former, chain transfer agent, and photoinitiator. Thefilm former, chain transfer agent, and photoinitiator collectivelydefine a second class of adhesive materials. In some embodiments of theinvention, the film former can include acrylates copolymer. In someembodiments of the invention, the chain transfer agent can includepentaerythrityl tetra mercaptopropionate. In some embodiments of theinvention, the photoinitiator can include trimethyl benzoyl diphenylphosphine oxide. In some embodiments of the invention, the bottomadhesive layer 116 includes a film former, chain transfer agent,photoinitiator, plasticizer, and photosensitizer. The plasticizer caninclude, for example, dimethicone. The photosensitizer can include, forexample, isopropyl thioxanthone. Forming the bottom adhesive layer 116from a film former, chain transfer agent, and photoinitiator in thismanner results in the bottom adhesive layer 116 having a UV-based drytime of about 60 seconds. Advantageously, a removal time of only about 3to 120 seconds can be achieved using only a water soak. The bottomadhesive layer 116 can be removed after the water soak by peeling orrubbing.

In some embodiments of the invention, the bottom adhesive layer 116includes a film former, solvent, and plasticizer. The film former,solvent, and plasticizer collectively define a third class of adhesivematerials. In some embodiments of the invention, the film former caninclude nitrocellulose, tosylamide-based resins, or formaldehyde-basedresins (e.g., tosylamide formaldehyde resin). In some embodiments of theinvention, the solvent can include ethyl acetate, butyl acetate, propylacetate, isopropyl alcohol, or diacetone alcohol. In some embodiments ofthe invention, the plasticizer can include trimethyl pentanyldiisobutyrate, triphenyl phosphate, ethyl tosylamide, or camphor. Insome embodiments of the invention, the bottom adhesive layer 116includes a film former, solvent, plasticizer, and diluent. The diluentcan include, for example, dimethicone. Forming the bottom adhesive layer116 from a film former, solvent, and plasticizer in this manner resultsin the bottom adhesive layer 116 having an air dry time of about 60 to300 seconds. Advantageously, a removal time of only about 10 to 120seconds can be achieved using an acetone soak. The bottom adhesive layer116 can be removed after the acetone soak by soaking or wiping.

An exemplary system 300 employing the electronic device 102 attached toa patient via the two-layer adhesive 112 is depicted schematically inFIG. 3 . In some embodiments of the invention, system 300 can include astrain gauge sensor and Wheatstone bridge circuit 302, an amplifier 304,an analog to digital converter module 306 that includes an analog todigital converter 306 a (i.e., ADC), a radio frequency (RF) controller306 b and a micro-controller 306 c, a network antenna 308, and aportable device 310. As further shown in FIG. 3 , the electronic device102 serves as a resistor in the Wheatstone bridge circuit 302. In someembodiments of the invention, the Wheatstone bridge circuit 302 receivespower from power supply 312. It is notable that the values (i.e., powersupply voltage, resistances, etc.) shown in FIG. 3 are merely given asexamples and not intended to in any way limit the embodiments to theseparticular values.

Amplifier 304 serves to amplify the (voltage) signal output from theWheatstone bridge circuit 302. Analog to digital converter 306 a (i.e.,ADC) in module 306 converts that amplified signal into a digital signal.Module 306 can also include a micro-controller 306 c (e.g., aprocessor—CPU) that prepares (e.g., conditions, buffers, etc.) thesignal for the radio frequency (RF) controller 306 b that then transfersthe digitized signals to a receiver.

Network antenna 308 transmits the digital signals from analog to digitalconverter 306. These digital signals are transmitted, for example, vianear-field communication (NFC), WiFi, Bluetooth® technology, etc. to oneor more user devices, such as a smartphone 314 (or other smart devicessuch as a smartwatch, smart glasses, etc.) and/or computer 316.

Turning now to FIG. 4 , a block diagram is shown of an apparatus 400 forimplementing one or more of the techniques presented herein. By way ofexample only, apparatus 400 can be configured to serve as themicro-controller 306 c and/or as one or more of the user devices (e.g.,smartphone 314, computer 316, etc.) of system 300 (FIG. 3 ).

In some embodiments of the invention, apparatus 400 includes a computersystem 410 and removable media 450. Computer system 410 includes aprocessor device 420, a network interface 425, a memory 430, a mediainterface 435 and an optional display 440. Network interface 425 allowscomputer system 410 to connect to a network, while media interface 435allows computer system 410 to interact with media, such as a hard driveor removable media 450.

The processor device 420 can be configured to implement the methods,steps, and functions described herein. The memory 430 can be distributedor local and the processor device 420 could be distributed or singular.The memory 430 could be implemented as an electrical, magnetic oroptical memory, or any combination of these or other types of storagedevices. Moreover, the term “memory” should be construed broadly enoughto encompass any information able to be read from, or written to, anaddress in the addressable space accessed by processor device 420. Withthis definition, information on a network, accessible through networkinterface 425, is still within memory 430 because the processor device420 can retrieve the information from the network. It should be notedthat each distributed processor that makes up processor device 420generally contains its own addressable memory space. It should also benoted that some or all of computer system 410 can be incorporated intoan application-specific or general-use integrated circuit.

In some embodiments of the invention, the optional display 440 caninclude any type of display suitable for interacting with a human userof apparatus 400. Generally, display 440 is a computer monitor, LCD orLED screen, or other similar display.

FIG. 5 depicts a flow diagram 500 illustrating a method for securing anelectronic device to a live nail using a two-layer adhesive according toone or more embodiments of the invention. As shown at block 502, asurface of the nail is coated with a first adhesive layer. In someembodiments of the invention, the first adhesive layer is selected froma first class of materials, a second class of materials, and a thirdclass of materials.

In some embodiments of the invention, the first adhesive layer includesa film former, a plasticizer, and a solubilizing agent (collectively thefirst class of materials). In some embodiments of the invention, thefilm former includes one of polyurethane-35, acrylic crosspolymer resin,and vinyl pyrrolidone (VP) crosspolymer resin. In some embodiments ofthe invention, the plasticizer includes glycerine and wherein thesolubilizing agent includes laureth-21.

In some embodiments of the invention, the first adhesive layer includesa film former, a chain transfer agent, and a photoinitiator(collectively the second class of materials). In some embodiments of theinvention, the film former includes an acrylates copolymer, the chaintransfer agent includes pentaerythrityl tetra mercaptopropionate, andthe photoinitiator includes trimethyl benzoyl diphenyl phosphine oxide.

In some embodiments of the invention, the first adhesive layer includesa film former, a solvent, and a plasticizer (collectively the thirdclass of materials). In some embodiments of the invention, the filmformer includes at least one of nitrocellulose, a tosylamide-basedresin, or a formaldehyde-based resin. In some embodiments of theinvention, the solvent includes one or more of ethyl acetate, butylacetate, propyl acetate, isopropyl alcohol, and diacetone alcohol. Insome embodiments of the invention, the plasticizer includes one or moreof trimethyl pentanyl diisobutyrate, triphenyl phosphate, ethyltosylamide, and camphor.

At block 504, the first adhesive layer is cured. In some embodiments ofthe invention, curing the first adhesive layer includes an air cure ofabout 30 to 300 seconds (e.g., for the first class of materials). Insome embodiments of the invention, curing the first adhesive layerincludes exposing the first adhesive layer to UV light for about 60(e.g., for the second class of materials). In some embodiments of theinvention, curing the first adhesive layer includes an air cure of about60 to 300 seconds (e.g., for the third class of materials).

At block 506, a surface of the cured first adhesive layer is coated witha second adhesive layer. In some embodiments of the invention, thesecond adhesive layer includes cyanoacrylate.

At block 508, an electronic device is positioned on the uncured secondadhesive layer (i.e., prior to curing the second adhesive layer). Atblock 510, the second adhesive layer is cured. In some embodiments ofthe invention, curing the second adhesive layer embeds the electronicdevice within the second adhesive layer or to the surface of the secondadhesive layer. In some embodiments of the invention, the secondadhesive layer is cured using an air cure of about 30 seconds, althoughother cure durations are within the contemplated scope of the inventiondepending on the particular material selected for the second adhesivelayer.

FIG. 6 depicts a flow diagram 600 illustrating a method for removing anelectronic device from a patient (e.g., a patient's live nail) using atwo-layer adhesive according to one or more embodiments of theinvention. As shown at block 602, an adhesive stack is formed on asurface of the patient.

In some embodiments of the invention, the adhesive stack releases uponexposure to a first solvent after a first duration and an electricdevice releases upon exposure to a second solvent after a secondduration more than the first duration. For example, the bottom layer canbe removed using water as a first solvent, and the cyanoacrylate toplayer can be removed using acetone as the second solvent. In otherwords, the whole adhesive stack including the organism surface, bottomlayer, top layer, and the electronic device will be exposed to the firstsolvent (e.g., water) for a set duration (e.g., 3 minutes). Exposure tothe first solvent minimizes the amount of bottom layer material leftoverand releases the remaining stack from the organism surface, exposing adiscrete stack of top layer (e.g., cyanoacrylate) and the electronicdevice. The second solvent exposure releases the electronic device fromthe top layer. As discussed previously, in some embodiments of theinvention, the second solvent exposure is done after separation from theorganism and can include an arbitrarily longer duration than the firstsolvent exposure (e.g., 5 minutes, 10 minutes, 30 minutes, hours, etc.).

In some embodiments of the invention, the adhesive stack releases uponexposure to a first solvent (e.g., acetone) after a first duration andthe electric device releases upon exposure to the first solvent (e.g.,acetone) after a second duration more than the first duration. In otherwords, complete separation can be achieved using two soaks in the samesolvent. For example, a relatively short soak in acetone can be used toremove the adhesive stack and electronic device from the surface of theorganism, and a second, relatively longer soak in acetone can be used toremove the top layer from the electronic device.

In some embodiments of the invention, the electronic device is releasedfrom the adhesive stack prior to removal of the adhesive stack from theorganism. In other words, in some embodiments of the invention, theadhesive stack is exposed to the second solvent prior to the firstsolvent.

In some embodiments of the invention, the top layer includescyanoacrylate. In some embodiments of the invention, the bottom layerincludes one or more of polyurethane-35, acrylic crosspolymer resin,vinyl pyrrolidone (VP) crosspolymer resin, an acrylates copolymer,nitrocellulose, a tosylamide-based resin, or a formaldehyde-based resin.

At block 604, the adhesive stack is exposed to the second solvent forthe second duration to release the adhesive stack from the surface ofthe patient. At block 606, the adhesive stack is removed from thepatient.

At block 608, after removing the adhesive stack, the adhesive stack isexposed to the second solvent for the second duration to separate theelectronic device from the top layer. In some embodiments of theinvention, the first solvent and the second solvent are the same. Insome embodiments of the invention, the first solvent includes water andthe second solvent includes acetone.

As can be seen from the foregoing detailed descriptions, technicaleffects and benefits of embodiments of the invention provide a newtwo-layer adhesive and methods of using the same to secure an electronicdevice to an organism (e.g., to a live nail of a patient). This newtwo-layer adhesive can be easily and quickly removed due to theinclusion of a temporary bottom layer, directly addressing theshortcomings of conventional adhesives (e.g., cyanoacrylate-basedadhesives). Advantageously, the top layer of the two-layer adhesive caninclude conventionally strong, long lasting adhesives such ascyanoacrylates (for binding the electronic device), while the bottomlayer can include an easily removable resin, such as one or more ofpolyurethane-35, acrylic crosspolymer resin, vinyl pyrrolidone (VP)crosspolymer resin, an acrylates copolymer, nitrocellulose, atosylamide-based resin, or a formaldehyde-based resin.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. Althoughvarious connections and positional relationships (e.g., over, below,adjacent, etc.) are set forth between elements in the followingdescription and in the drawings, persons skilled in the art willrecognize that many of the positional relationships described herein areorientation-independent when the described functionality is maintainedeven though the orientation is changed. These connections and/orpositional relationships, unless specified otherwise, can be direct orindirect, and the present invention is not intended to be limiting inthis respect. Similarly, the term “coupled” and variations thereofdescribes having a communications path between two elements and does notimply a direct connection between the elements with no interveningelements/connections between them. All of these variations areconsidered a part of the specification. Accordingly, a coupling ofentities can refer to either a direct or an indirect coupling, and apositional relationship between entities can be a direct or indirectpositional relationship. As an example of an indirect positionalrelationship, references in the present description to forming layer “A”over layer “B” include situations in which one or more intermediatelayers (e.g., layer “C”) is between layer “A” and layer “B” as long asthe relevant characteristics and functionalities of layer “A” and layer“B” are not substantially changed by the intermediate layer(s).

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as anexample, instance or illustration.” Any embodiment or design describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” are understood to include any integer number greaterthan or equal to one, i.e. one, two, three, four, etc. The terms “aplurality” are understood to include any integer number greater than orequal to two, i.e. two, three, four, five, etc. The term “connection”can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment may or may not include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the described structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on top,” “positioned on” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements such as an interfacestructure can be present between the first element and the secondelement. The term “direct contact” means that a first element, such as afirst structure, and a second element, such as a second structure, areconnected without any intermediary conducting, insulating orsemiconductor layers at the interface of the two elements.

Spatially relative terms, e.g., “beneath,” “below,” “lower,” “above,”“upper,” and the like, are used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (e.g., rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein should be interpreted accordingly.

The terms “about,” “substantially,” “approximately,” and variationsthereof, are intended to include the degree of error associated withmeasurement of the particular quantity based upon the equipmentavailable at the time of filing the application. For example, “about”can include a range of ±8% or 5%, or 2% of a given value.

The present invention may include a system, a method, and/or a computerprogram product at any possible technical detail level of integration.The computer program product may include a computer readable storagemedium (or media) having computer readable program instructions thereonfor causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, configuration data for integrated circuitry, oreither source code or object code written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Smalltalk, C++, or the like, and procedural programminglanguages, such as the “C” programming language or similar programminglanguages. The computer readable program instructions may executeentirely on the user's computer, partly on the user's computer, as astand-alone software package, partly on the user's computer and partlyon a remote computer or entirely on the remote computer or server. Inthe latter scenario, the remote computer may be connected to the user'scomputer through any type of network, including a local area network(LAN) or a wide area network (WAN), or the connection may be made to anexternal computer (for example, through the Internet using an InternetService Provider). In some embodiments, electronic circuitry including,for example, programmable logic circuitry, field-programmable gatearrays (FPGA), or programmable logic arrays (PLA) may execute thecomputer readable program instruction by utilizing state information ofthe computer readable program instructions to personalize the electroniccircuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the Figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdescribed herein

What is claimed is:
 1. A method for removing an electronic device froman organism, the method comprising: forming an adhesive stack on asurface of the organism, the adhesive stack comprising a bottom layerpositioned between a top layer and the surface of the organism, theelectronic device embedded in the top layer, wherein the bottom layerreleases upon exposure to a first solvent after a first duration and thetop layer releases upon exposure to a second solvent after a secondduration more than the first duration; exposing the adhesive stack tothe first solvent for the first duration to release the adhesive stackfrom the surface of the organism; and removing the adhesive stack fromthe organism.
 2. The method of claim 1, wherein the first solvent andthe second solvent are the same.
 3. The method of claim 1, wherein thesecond solvent comprises acetone and the first solvent comprises water.4. The method of claim 1 further comprising, after removing the adhesivestack from the organism, exposing the adhesive stack to the secondsolvent for the second duration to separate the electronic device fromthe top layer.
 5. The method of claim 1, wherein the top layer comprisescyanoacrylate and the bottom layer comprises one or more ofpolyurethane-35, acrylic crosspolymer resin, vinyl pyrrolidone (VP)crosspolymer resin, an acrylates copolymer, nitrocellulose, atosylamide-based resin, or a formaldehyde-based resin.
 6. The method ofclaim 1, wherein the surface of the organism is selected from the groupconsisting of a fingernail, a toenail, a tooth, a claw, a hoof, and anarea of skin.
 7. The method of claim 1, wherein the electronic devicecomprises at least one of a wearable sensor, a strain gauge, anaccelerometer, a photoplethysmogram (PPG), an electrocardiogram (ECG),an electroencephalography (EEG), a temperature sensor, a respirationsensor, a gyroscope, a piezoelectric sensor, a heart-monitoring device,a glucose-monitoring device, and a transcutaneous electrical nervestimulation (TENS) electrode therapy device.
 8. The method of claim 1,wherein the bottom layer comprises: a film former; a plasticizer; and astabilizer.
 9. The method of claim 8, wherein the film former comprisesone of polyurethane-35 and an acrylic or vinyl pyrrolidone (VP)crosspolymer resin, the plasticizer comprises glycerine, and thestabilizer comprises laureth-21.
 10. The method of claim 9, wherein thefirst solvent comprises water and the first duration comprises 3 to 120seconds.
 11. The method of claim 1, wherein the bottom layer comprises:a film former; a chain transfer agent; and a photoinitiator.
 12. Themethod of claim 11, wherein the film former comprises an acrylatescopolymer, the chain transfer agent comprises pentaerythrityl tetramercaptopropionate, and the photoinitiator comprises trimethyl benzoyldiphenyl phosphine oxide.
 13. The method of claim 12, wherein the filmformer further comprises a plasticizer and a photosensitizer, whereinthe plasticizer comprises dimethicone and the photosensitizer comprisesisopropyl thioxanthone.
 14. The method of claim 13, wherein the firstsolvent comprises water and the first duration comprises 3 to 120seconds.
 15. The method of claim 1, wherein the bottom layer comprises:a film former; a solvent; and a plasticizer.
 16. The method of claim 15,wherein the film former comprises at least one of nitrocellulose, atosylamide-based resin, and a formaldehyde-based resin, the solventcomprises at least one of ethyl acetate, butyl acetate, propyl acetate,isopropyl alcohol, and diacetone alcohol, and the plasticizer comprisesat least one of trimethyl pentanyl diisobutyrate, triphenyl phosphate,ethyl tosylamide, and camphor.
 17. The method of claim 16, wherein thefirst solvent comprises acetone and the first duration comprises 10 to120 seconds.
 18. An adhesive stack for securing an electronic device toan organism, the adhesive stack comprising: a top layer; a bottom layerpositioned between the top layer and a surface of the organism; and anelectronic device embedded in the top layer; wherein the bottom layerreleases upon exposure to a first solvent after a first duration and thetop layer releases upon exposure to a second solvent after a secondduration greater than the first duration.
 19. The adhesive stack ofclaim 18, wherein the top layer comprises cyanoacrylate.
 20. Theadhesive stack of claim 18, wherein the bottom layer comprises one ormore of polyurethane-35, acrylic crosspolymer resin, vinyl pyrrolidone(VP) crosspolymer resin, an acrylates copolymer, nitrocellulose, atosylamide-based resin, or a formaldehyde-based resin.